Einsteinium — (Albert Einstein [1879–1955]),
Es; at. wt. (252);
m.p. 860 °C (est.); at. no. 99. Einsteinium, the seventh tran-
The Elements 4-11
suranic element of the actinide series to be discovered, was
identified by Ghiorso and co-workers at Berkeley in December
1952 in debris from the first large thermonuclear explosion,
which took place in the Pacific in November 1952. The isotope
produced was the 20-day 253Es isotope. In 1961, a sufficient
amount of einsteinium was produced to permit separation of
a macroscopic amount of 253Es. This sample weighed about
0.01 μg. A special magnetic-type balance was used in making
this determination. 253Es so produced was used to produce
mendelevium. About 3 μg of einsteinium has been produced
at Oak Ridge National Laboratories by irradiating for several
years kilogram quantities of 239Pu in a reactor to produce 242Pu.
This was then fabricated into pellets of plutonium oxide and
aluminum powder, and loaded into target rods for an initial
1-year irradiation at the Savannah River Plant, followed by
irradiation in a HFIR (High Flux Isotopic Reactor). After 4
months in the HFIR the targets were removed for chemical
separation of the einsteinium from californium. Nineteen isotopes
and isomers of einsteinium are now recognized. 254Es
has the longest half-life (276 days). Tracer studies using 253Es
show that einsteinium has chemical properties typical of a
heavy trivalent, actinide element. Einsteinium is extremely radioactive.
Great care must be taken when handling it.